In Plato’s Timaeus, two different theories – the Receptacle theory and the geometrical particle theory – are presented to explain change in the natural world. In this paper, I argue that there is tension between the two theories. After examining several possible solutions for this tension, I conclude that Plato does not present it as something ready to be solved within the dialogue but, rather, as something to be understood in a way that maintains both theories. Finally, I also argue (...) that the contrast between the two theories in the Timaeus derives from a similar contrast in the Phaedo. (shrink)